This invention relates to a conjugated diene-based rubber composition reinforced with particulate alumina in combination with a non-silane coupling agent as a high purity tetrathiodipropionic acid and/or trithiodipropionic acid. The invention includes an article of manufacture, including a tire, having at least one component comprised of such rubber composition.
For various applications utilizing rubber compositions, carbon black and/or synthetic amorphous silica-based materials are conventionally used as particulate reinforcing fillers for the elastomer(s) of the rubber composition(s).
Often an organosilane-based coupling agent such as, for example, an organoalkoxysilane-based polysulfide coupling agent is used together with precipitated silica or with alumina in order to couple, or otherwise enhance, its elastomer reinforcement effect for the elastomer(s) and such use of a coupling agent is well known to those having skill in such art (e.g. a bis(3-triethoxysilylpropyl)polysulfide having an average of from 2 to 2.6 or from 3.5 to 4 connecting sulfur atoms in its polysulfidic bridge.
However, use of such alkoxysilane-based silane coupling agent normally results in a release of an alcohol (e.g. ethanol), as a byproduct, by reaction of the alkoxy groups of the silane with hydroxyl groups contained on the surface of aggregates of synthetic precipitated silica, particularly during a rubber mixing process where rubber, precipitated silica and such type of coupling agent are mixed together.
For various purposes, it may be desired to reduce or substantially eliminate, or even entirely eliminate such alcohol evolution while mixing with various rubber compositions.
It is also appreciated that particulate alumina, particularly a natural occurring alumina such as, for example, Boehmite alumina as an aluminum oxide hydroxide comprised of the general formula: Al2O3xc2x7xH2O, has heretofore been proposed for blending with various rubber compositions where the xe2x80x9cxxe2x80x9d indicates that water of hydration is contained on or with the aluminum oxide in an amount of xe2x80x9cxxe2x80x9d units of water which can vary significantly such as for example only, from one to perhaps three or more units of water. Such water of association is well known to those having skill in such art. It is considered herein that such alumina contains hydroxyl groups on its surface.
In the description of this invention, the term xe2x80x9cphrxe2x80x9d is used to designate parts by weight of a material per 100 parts by weight of elastomer. In the further description, the terms xe2x80x9crubberxe2x80x9d and xe2x80x9celastomerxe2x80x9d may be used interchangeably unless otherwise mentioned. The terms xe2x80x9cvulcanizedxe2x80x9d and xe2x80x9ccuredxe2x80x9d may be used interchangeably, as well as xe2x80x9cunvulcanizedxe2x80x9d or xe2x80x9cuncuredxe2x80x9d, unless otherwise indicated.